Investigations of the highly efficient processing technique, chemical constituents, and anti-inflammatory effect of N-ethyl-2-pyrrolidinone-substituted flavan-3-ol (EPSF)-enriched white tea.

N-Ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) are a newly discovered compound class in tea with various bioactivities. This study aimed to develop a novel processing technique to enhance EPSF contents in white tea efficiently. Using optimal processing parameters of 125 °C and 30 min in a high-temperature sterilizing oven, total EPSF content significantly increased by 1.42-18.80-fold to 1.57-6.22 mg/g without impacting sensory characteristics. Metabolomics analysis revealed elevated levels of nucleosides, nucleotides, bases, theaflavins, flavonol aglycones, EPSFs, and most flavone-C-glycosides, as well as decreased levels of amino acids, procyanidins, theasinensins, several flavanols, and flavonol-O-glycosides after EPSF-enrichment treatment. Furthermore, the EPSF-enriched white tea exhibited notable anti-inflammatory effects, mitigating xylene-induced ear edema in mice and carrageenan-induced paw edema and cotton ball-induced granulomas in rats. This study developed a new processing technique for highly efficient enhancement of EPSFs in white tea and demonstrated that EPSF-enriched white tea has a potential to serve as effective anti-inflammatory dietary supplement.

Structural characterization and high-efficiency prebiotic activity of the polysaccharide from Tremella aurantialba endophytic bacteria.

Herein, the low-molecular-weight heteropolysaccharide (designated as TABP), with a weight-average Mw of 5408 Da, was produced by the endophytic bacterium Bacillus sp. TAB, which was initially isolated from the fruiting bodies of the wild Tremella aurantialba. A relatively high TABP accumulation was obtained and enhanced to 6.94 g/L in 5 L fed-batch fermentation by high-density cultivation. Monosaccharide composition analysis showed that the TABP comprised arabinose, glucosamine, galactose, glucose, and mannose with a molar ratio of 0.073: 0.145: 0.406: 0.182: 0.195, respectively. Methylation and NMR analyses indicated that TABP contained 1,4-linked ß-d-Galp and 1,4-linked ß-d-Manp pyranosyl backbone, extensively substituted at the side chains to form a complex structure. Prebiotic potential analysis exhibited significant growth-promoting effects for various lactic acid bacteria by more than 90 %. Overall, this study initially provides valuable insights into the endophytic exopolysaccharides from T. aurantialba and their biological activity, which provides prospective sources of prebiotics for functional foods and aids in understanding the endophytes symbiosis mechanism in edible mushrooms.

Improved Stability and In Vitro Anti-Arthritis Bioactivity of Curcumin-Casein Nanoparticles by Ultrasound-Driven Encapsulation.

Curcumin possesses beneficial biological functions, namely anti-inflammation and anti-diabetic functions. However, due to its low solubility and crystallinity, its applications are limited. In this work, curcumin was encapsulated in casein micelles in order to form curcumin-casein nanoparticles by ultrasound treatment (5 min). The ultrasound treatment induced the entry of the hydrophobic groups to the inner micelles and the polar sulfydryl groups to the surface of the micelles in order to form compact curcumin-casein nanoparticles of an appropriate size (100-120 nm) for cellular endocytosis. The product exhibited excellent stability during 8 months of cold storage, 6 days at room temperature, and 2 days at body temperature. Advanced in vitro experiments demonstrated that curcumin-casein nanoparticles displayed significantly greater inhibitory activity against the proliferation and proinflammatory cytokines of human fibroblast-like synoviocyte-osteo arthritis (HFLS-OA) cells and HFLS-rheumatoid (RA) cells than native curcumin due to better cellular uptake as a result of the low crystallinity and the appropriate nano-size of the nano-form. The results provide a reference for the use of ultrasound treatment to encapsulate other drug molecules and curcumin-casein nanoparticles as potential treatment for arthritis.

Insights into Characteristic Volatiles in Wuyi Rock Teas with Different Cultivars by Chemometrics and Gas Chromatography Olfactometry/Mass Spectrometry.

Wuyi rock tea (WRT) is one of the most famous subcategories of oolong tea, exhibiting distinct aroma characteristics with the application of different cultivars. However, a comprehensive comparison of the characteristic volatiles among WRTs with different cultivars has rarely been carried out. In this study, non-targeted analyses of volatile fragrant compounds (VFCs) and targeted aroma-active compounds in WRTs from four different cultivars were performed using chemometrics and gas chromatography olfactometry/mass spectrometry (GC-O/MS). A total of 166, 169, 166, and 169 VFCs were identified for Dahongpao (DHP), Rougui (RG), Shuixian (SX), and Jinfo (JF), respectively; and 40 components were considered as the key differential VFCs among WRTs by multivariate statistical analysis. Furthermore, 56 aroma-active compounds were recognized with predominant performances in "floral & fruity", "green & fresh", "roasted and caramel", "sweet", and "herbal" attributes. The comprehensive analysis of the chemometrics and GC-O/MS results indicated that methyl salicylate, p-cymene, 2,5-dimethylpyrazine, and 1-furfurylpyrrole in DHP; phenylethyl alcohol, phenethyl acetate, indole, and (E)-ß-famesene in RG; linalool, phenethyl butyrate, hexyl hexanoate, and dihydroactinidiolide in JF; and naphthalene in SX were the characteristic volatiles for each type of WRT. The obtained results provide a fundamental basis for distinguishing tea cultivars, recombination, and simulation of the WRT aroma.

Metabolomic characterization of the chemical compositions of Dracocephalum rupestre Hance.

Maojian tea (MJT) is a traditional Chinese herbal tea beverage manufactured from the leaves of the Dracocephalum rupestre Hance plant. In this study, a nontargeted metabolomics approach combined with absolute quantifications was applied to comprehensively investigate the chemical compositions of MJT and to determine the effects of the processing methods on compounds. Flavones (apigenin and luteolin, 0.06-1.35 mg/g), flavanones (eriodictyol and naringenin, 0.1-2.3 mg/g), flavone 7-O-glycosides (0.15-5.98 mg/g), flavanone 7-O-glycosides (0.28-19.41 mg/g), and triterpenoids were presumed to be characteristic components of MJT. Applying imitative green and black tea processing methods to MJT led to increases in flavone/flavanone aglycones, lipids, and triterpenoids and decreases in flavone/flavanone glycosides, amino acids, organic acids, and most phenolic acids. This study offers novel insights into the chemical compositions and the influences of processing methods on MJT and will be utilized for the quality control of MJT.

Hyaluronan Oligosaccharides-Coated Paclitaxel-Casein Nanoparticles with Enhanced Stability and Antitumor Activity.

This study aims to develop specific-molecular-weight hyaluronic acid oligosaccharides-coated paclitaxel-loaded casein nanoparticles (HA-PT-Cas NPs) via chemical conjugation to increase the stability and antitumor effects. Optimized HA-PT-Cas NPs (HA/casein of 3:1) were obtained with a mean size of 235.3 nm and entrapment efficiency of 93.1%. HA-PT-Cas exhibited satisfactory stability at 4 °C for 12 days and 37 °C for 3 h; paclitaxel was retained at rates of 81.4% and 64.7%, respectively, significantly higher than those of PT-Cas (only 27.8% at 4 °C after 16 h and 20.3% at 37 °C after 3 h). HA-PT-Cas exhibited high efficiency (61.3%) in inhibiting A375 tumor owing to the enhanced stability of HA oligosaccharides barrier, which was comparable with that of 10 µg/mL cis-platinum (64.9%). Mice experiments showed the 74.6% tumor inhibition of HA-PT-Cas by intravenously administration, significantly higher than that of PT-casein (39.8%). Therefore, this work provides an effective carrier for drug delivery via HA oligomers-coated modification.

The Effect of Microwave Radiation on the Green Color Loss of Green Tea Powder.

Microwave radiation is one of the main heating methods for food processing, especially affecting the color quality of colorful foods. This work presents the effect of microwave radiation on the green color loss of green tea powder (GTP) by the color description (L*, a*, b*, and Ha of green tea powder, L*:whiteness/darkness, a*: redness/greenness, and b*: yellowness/blueness; Ha derived from Hunter a and b could visually describe the color space) of the Hunter color system. First, the L*, a*, and b* were determined from the GTP samples treated with various microwave powers with the change of time to investigate the kinetic of color loss. Then, the L*, a*, and b*and temperature of GTP samples with serious thickness treated with constant microwave power (700 W) for a different time were determined to study the effect of sample thickness on the color loss. Finally, the chemicals that contributed to color change in the GTP samples treated with mild, moderate, and severe radiation were analyzed. The results showed that L*, |a*| (|a*|was the absolute value of a*), b*, and Ha decreased with the power increase in microwave radiation, and their changes conformed to the first-order kinetics. The activation energies (Ea) of different thickness GTP for change of L*, a*, b*, and Ha values could be predicted with the fitting models, and Ea for 20 mm-thick GTP were approximately 1/5, 1/8, 1/8, and 1/13 of those for 4 mm-thick GTP. The color loss was mainly caused by the Mg2+ loss of chlorophylls and the formation of derivates under mild radiation, the degradation of chlorophylls and the formation of theaflavin from catechins under moderate radiation, and the degradation of chlorophylls and their derivates accompanied by Maillard reaction between reducing sugar and amino acids under severe radiation. The results indicate that sample thickness and radiation time are two key parameters to keeping the color of GTP in food processing and microwave pasteurization.

Isolation of N-Ethyl-2-pyrrolidinone-Substituted Flavanols from White Tea Using Centrifugal Countercurrent Chromatography Off-Line ESI-MS Profiling and Semi-Preparative Liquid Chromatography.

N-Ethyl-2-pyrrolidinone-substituted flavanols (EPSF) are marker compounds for long-term stored white teas. However, due to their low contents and diasteromeric configuration, EPSF compounds are challenging to isolate. In this study, two representative epimeric EPSF compounds, 5'''R- and 5'''S-epigallocatechin gallate-8-C N-ethyl-2-pyrrolidinone (R-EGCG-cThea and S-EGCG-cThea), were isolated from white tea using centrifugal partition chromatography (CPC). Two different biphasic solvent systems composed of 1. N-hexane-ethyl acetate-methanol-water (1:5:1:5, v/v/v/v) and 2. N-hexane-ethyl acetate-acetonitrile-water (0.7:3.0:1.3:5.0, v/v/v/v) were used for independent pre-fractionation experiments; 500 mg in each separation of white tea ethyl acetate partition were fractionated. The suitability of the two solvent systems was pre-evaluated by electrospray mass-spectrometry (ESI-MS/MS) analysis for metabolite distribution and compared to the results of the CPC experimental data using specific metabolite partition ratio KD values, selectivity factors α, and resolution factors RS. After size-exclusion and semi-preparative reversed-phase liquid chromatography, 6.4 mg of R-EGCG-cThea and 2.9 mg of S-EGCG-cThea were recovered with purities over 95%. Further bioactivity evaluation showed that R- and S-EGCG-cThea possessed in vitro inhibition effects on α-glucosidase with IC50 of 70.3 and 161.7 µM, respectively.

Metabolomics Analysis Reveals Four Novel N-Ethyl-2-pyrrolidinone-Substituted Theaflavins as Storage-Related Marker Compounds in Black Tea.

Tea market is currently oversupplied, and unsold tea often needs to be properly stored for a period of time. However, the chemical changes occurring in black tea during storage are limitedly understood. In this study, a comprehensive nontargeted and targeted metabolomics approach was used to investigate the dynamic changes in compounds in time-series (0-19 months)-stored black teas. The contents of flavanols, theaflavins (TFs), theasinensins, procyanidins, most phenolic acids, amino acids, quercetin-O-glycosides, and myricetin-O-glycosides decreased during storage, while the contents of N-ethyl-2-pyrrolidinone-substituted flavanols, flavone-C-glycosides, and most kaempferol-O-glycosides increased. More importantly, four novel compounds strongly positively correlated with storage duration (r = 0.922-0.969) were structurally assigned as N-ethyl-2-pyrrolidinone-substituted TFs and validated with synthetic reactions of TFs and theanine standards. The content of N-ethyl-2-pyrrolidinone-substituted TFs was 51.54 µg/g in black tea stored for 19 months. To the best of our knowledge, N-ethyl-2-pyrrolidinone-substituted TFs were discovered in tea for the first time.

Identification of Aroma Composition and Key Odorants Contributing to Aroma Characteristics of White Teas.

The identification of aroma composition and key odorants contributing to aroma characteristics of white tea is urgently needed, owing to white tea's charming flavors and significant health benefits. In this study, a total of 238 volatile components were identified in the three subtypes of white teas using headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS). The multivariate statistical analysis demonstrated that the contents of 103 volatile compounds showed extremely significant differences, of which 44 compounds presented higher contents in Baihaoyinzhen and Baimudan, while the other 59 compounds exhibited higher contents in Shoumei. The sensory evaluation experiment carried out by gas chromatography-olfactometry/mass spectrometry (GC-O/MS) revealed 44 aroma-active compounds, of which 25 compounds were identified, including 9 alcohols, 6 aldehydes, 5 ketones, and 5 other compounds. These odorants mostly presented green, fresh, floral, fruity, or sweet odors. Multivariate analyses of chemical characterization and sensory evaluation results showed that high proportions of alcohols and aldehydes form the basis of green and fresh aroma characteristic of white teas, and phenylethyl alcohol, γ-Nonalactone, trans-ß-ionone, trans-linalool oxide (furanoid), α-ionone, and cis-3-hexenyl butyrate were considered as the key odorants accounting for the different aroma characteristics of the three subtypes of white tea. The results will contribute to in-depth understand chemical and sensory markers associated with different subtypes of white tea, and provide a solid foundation for tea aroma quality control and improvement.

N-Ethyl-2-Pyrrolidinone-Substituted Flavan-3-Ols with Anti-inflammatory Activity in Lipopolysaccharide-Stimulated Macrophages Are Storage-Related Marker Compounds for Green Tea.

Fresh green tea (GT) is commonly considered to have better sensory flavor and higher commercial value than long-term-stored GT; however, the chemical variations during storage are unclear. In this study, the chemical profiles of stored GT were surveyed among time-series samples from 0 to 19 months using a nontargeted metabolomics method. Seven N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) increased from 0.022 ± 0.019 to 3.212 ± 0.057 mg/g within 19 months (correlation coefficients with storage duration ranging from 0.936 to 0.965), and they were the most significantly increased compounds among the 127 identified compounds. Two representative EPSFs (R-EGCG-cThea and S-EGCG-cThea) possess potential anti-inflammatory properties by suppressing the expression, phosphorylation, and nuclear translocation of nuclear factor kappa-B (NF-κB) p65 in lipopolysaccharide-stimulated macrophages based on western blotting and immunofluorescence results. In conclusion, EPSFs were found to be marker compounds for stored GT and showed potential anti-inflammatory activity by regulating the NF-κB signaling pathway.

A novel spatial-resolution targeted metabolomics method in a single leaf of the tea plant (Camellia sinensis).

In this study, a novel spatial-resolution targeted metabolomics method was developed for a single leaf on the basis of microscale sample preparation and dansylation derivatization coupled with ultraperformance liquid chromatography-tandem mass spectrometry with a spatial resolution of 1.7 × 1.7 mm2. The practicability of this method was demonstrated by providing absolute quantitative within-leaf distribution information for 56 endogenous metabolites (including 8 catechins, 2 alkaloids, theanine, 4 theaflavins, 14 flavonol/flavone and their glycosides, 21 amino acids, and 6 phenolic acids). An application of this method in a mechanically pierced tea leaf indicated that astringent catechins, quercetin, and quercetin glycosides may be involved in the tea plant response to the wounding. In conclusion, the proposed novel method offered richest information on the within-leaf distribution of metabolites in tea to date and will be greatly helpful in understanding the defensive responses of tea plants against biotic and abiotic stresses.

Nontargeted metabolomics predicts the storage duration of white teas with 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols as marker compounds.

Storage has a dramatic influence on the chemical composition, sensory qualities, biological activity, and therefore the commercial value of white tea. In this study, the metabolites in white teas stored for 1, 3, 7, and ≥ 10 years were comprehensively compared by a nontargeted metabolomics investigation. Most metabolites, including catechins, flavonol/flavone glycosides, amino acids, nucleosides, organic acids, aroma precursors, lipids, and carbohydrates, decreased with increasing storage duration, while 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) and pyroglutamic acid increased. The absolute quantifications of 24 storage-related compounds combined with linear regression analysis showed that a panel of 5 indexes based on EPSFs has a good predictive ability for the storage duration of white teas (correlation coefficients were 0.9294 and 0.8812 in the model and test sets, respectively). The errors between the predicted and the actual storage durations ranged from -1.75 to 1.84 years for the white teas stored for <10 years.

Methyl Jasmonate-Induced Changes of Flavor Profiles During the Processing of Green, Oolong, and Black Tea.

Tea aroma is one of the most important factors affecting the character and quality of tea. Here we describe the practical application of methyl jasmonate (MeJA) to improve the aroma quality of teas. The changes of selected metabolites during crucial tea processing steps, namely, withering, fixing and rolling, and fermentation, were analyzed. MeJA treatment of tea leaves (12, 24, 48, and 168 h) greatly promotes the aroma quality of green, oolong, and black tea products when comparing with untreated ones (0 h) and as confirmed by sensory evaluation. MeJA modulates the aroma profiles before, during, and after processing. Benzyl alcohol, benzaldehyde, 2-phenylethyl alcohol, phenylacetaldehyde, and trans-2-hexenal increased 1.07- to 3-fold in MeJA-treated fresh leaves and the first two maintained at a higher level in black tea and the last two in green tea. This correlates with a decrease in aromatic amino acids by more than twofold indicating a direct relation to tryptophan- and phenylalanine-derived volatiles. MeJA-treated oolong tea was characterized by a more pleasant aroma. Especially the terpenoids linalool and oxides, geraniol, and carvenol increased by more than twofold.

Variation patterns in the content of glycosides during green tea manufacturing by a modification-specific metabolomics approach: Enzymatic reaction promoting an increase in the glycosidically bound volatiles at the pan firing stage.

The glycosides are presumed to influence the quality of green tea but the molecular mechanism behind remains unclear. To elucidate the contribution of glycosides to the flavor formation of green tea, changes of both glycosidically bound non-volatiles (GBNVs) and glycosidically bound volatiles (GBVs) during the manufacturing of green tea were investigated using a modification-specific metabolomics method. A total of 64 glycosides (47 GBNVs and 17 GBVs) were identified and their contents mainly changed during the pan firing and drying stages of green tea manufacturing. Notably, the contents of GBVs significantly increased by 1.12-4.46-fold during pan firing. Correlation analysis showed that the GBVs contents were negatively related to the contents of volatiles and glucose. Model experiments revealed that enzymatic synthesis contributed to the increase in the content of GBVs during the pan firing. This comprehensive study on the glycosides changes revealed the molecular bases for GBVs increments during the pan firing.

Metabolomics Investigation Reveals That 8-C N-Ethyl-2-pyrrolidinone-Substituted Flavan-3-ols Are Potential Marker Compounds of Stored White Teas.

White teas of different stored ages have varied flavor, bioactivity, and commercial value. In this study, a liquid chromatography-mass spectrometry-based metabolomics investigation revealed that there are distinct differences among the compound patterns of Baihaoyinzhen (BHYZ) and Baimudan (BMD) white teas with various storage durations. The levels of flavan-3-ols, procyanidins, theasinensins, theaflavins, flavonol- O-glycosides, flavone- C-glycosides, and most of the amino acids were reduced after long-term (>4 years) storage. More importantly, 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs), including seven novel compounds discovered in white teas for the first time, were formed from theanine and flavan-3-ols during storage, and their contents were positively correlated with the storage duration. These findings were further confirmed by the linearly increasing formation of EPSFs in reaction solution and BMD white teas stored in an environment-controlled cabinet. In conclusion, EPSFs were detected in white teas for the first time and were discovered as marker compounds and potential indicators for long-term storage of white tea.

Metabolomic analysis reveals the composition differences in 13 Chinese tea cultivars of different manufacturing suitabilities.

BACKGROUND: Green tea and black tea are manufactured using appropriate tea cultivars in China. However, the metabolite differences relating to the manufacturing suitability of tea cultivars are unclear. In the present study, we performed a non-targeted metabolomic analysis on 13 Chinese tea cultivars using ultra-high performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry to investigate comprehensively the metabolite differences between cultivars suitable for manufacturing green tea (GT cultivars) and cultivars suitable for manufacturing both green tea and black tea (G&BT cultivars). RESULTS: Multivariate statistical analysis and cluster analysis divided the 13 cultivars into two groups, namely GT cultivars and G&BT cultivars, which correlated with their manufacturing suitability. The GT cultivars contained higher levels of flavonoid glycosides, whereas the G&BT cultivars contained higher levels of catechins, dimeric catechins, phenolic acids and alkaloids. CONCLUSION: Metabolic pathway analysis revealed that the flavonoid pathway inclined toward the synthesis of flavonoid glycosides in GT cultivars, whereas it inclined toward the synthesis of catechins and phenolic acids in G&BT cultivars. The results of the present study will be helpful for discriminating the manufacturing suitability of tea cultivars and investigating their breeding. © 2017 Society of Chemical Industry.

Characterization of white tea metabolome: Comparison against green and black tea by a nontargeted metabolomics approach.

White tea is considered the least processed form of tea and is reported to have a series of potent bioactivities, such as antioxidant, anti-inflammatory, anti-mutagenic, and anti-cancer activities. However, the chemical composition of white tea and the dynamic changes of the metabolites during the manufacturing process are far from clear. In this study, we applied a nontargeted metabolomics approach based on ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS) to comprehensively profile the characteristic metabolites of white tea. There were significant differences in the content of amino acids, catechins, dimeric catechins, flavonol and flavone glycosides, and aroma precursors in white tea compared with green and black teas that were manufactured from the same fresh tea leaves. Furthermore, the dynamic changes of the metabolites in the tea samples with various withering durations of 0, 4, 8, 12, 16, 20, 24, 28, and 36 h were also profiled. This study offers a comprehensive characterization of the metabolites and their changes in white tea.

Nontargeted Modification-Specific Metabolomics Investigation of Glycosylated Secondary Metabolites in Tea (Camellia sinensis L.) Based on Liquid Chromatography-High-Resolution Mass Spectrometry.

Glycosylation on small molecular metabolites modulates a series of biological events in plants. However, a large number of glycosides have not been discovered and investigated using -omics approaches. Here, a general strategy named "nontargeted modification-specific metabolomics" was applied to map the glycosylation of metabolites. The key aspect of this method is to adopt in-source collision-induced dissociation to dissociate the glycosylated metabolite, causing a characteristic neutral loss pattern, which acts as an indicator for the glycosylation identification. In an exemplary application in green teas, 120 glucosylated/galactosylated, 38 rhamnosylated, 21 rutinosylated, and 23 primeverosylated metabolites were detected simultaneously. Among them, 61 glycosylated metabolites were putatively identified according to current tea metabolite databases. Thanks to the annotations of glycosyl moieties in advance, the method aids metabolite identifications. An additional 40 novel glycosylated metabolites were tentatively elucidated. This work provides a feasible strategy to discover and identify novel glycosylated metabolites in plants.

Nontargeted Analysis Using Ultraperformance Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry Uncovers the Effects of Harvest Season on the Metabolites and Taste Quality of Tea (Camellia sinensis L.).

The chemical composition and taste quality of tea fluctuate seasonally. However, the compounds responsible for the seasonal variation of metabolic pattern and taste quality are far from clear. This study compared the metabolite profiles of green teas of nine varieties that were plucked in spring, summer, and autumn by using ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) on a reversed phase column. A multivariate analysis indicated distinct differences among the metabolite phenotypes of teas harvested in different seasons. Heat-map analysis and metabolic pathway analysis demonstrated that flavan-3-ols, theasinensins, procyanidins, quercetin-O-glycosides, apigenin-C-glycosides, and amino acids exhibited sharp seasonal fluctuations. An equivalent quantification of tea tastes showed that in summer and autumn teas, the bitterness and astringency were significantly elevated, whereas umami declined. Metabolite content comparisons and partial least-squares analysis suggested that several flavonoids and amino acids are mainly responsible for the seasonal variations in taste quality.